The Puzzle of Slave Heights in Antebellum America

Ray Rees*, Munich, John Komlos, Munich, Ulrich Woitek, Glasgow, and N.V. Long, Montreal
*Seminar fuer Wirtschaftsgeschichte
University of Munich
Ludwigstrasse 33-IV
80539 Germany
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The diverging trends in physical stature and in real income of the free population of the Antebellum United States have both puzzled and fascinated economic historians (Fogel, 1994; Komlos, 1992; Komlos, 1996; Margo and Steckel, 1992; Steckel, 1995a). One would hardly have expected adult men to become 2 cm shorter within a generation prior to the Civil War when per capita income was growing at the respectable rate of 1.4 percent per annum (Weiss, 1992). The Afro-American experience is of particular interest in this context, since there is accumulating evidence to suggest that, in contrast to the trend for the free population, both white and black, the terminal height of the male birth cohorts of slaves of the 1830's and 1840's was increasing, while that of females and boys tended either to remain unchanged or to diminish only slightly (Steckel, 1995b; Komlos and Coclanis, 1997). Inasmuch as this pattern has been found in two separate sample of slaves, one based on Georgia convicts and the other on slaves shipped in interregional trade from the Upper to the Lower South, it is unlikely to be a statistical artefact.

We argue that this anomaly can be explained as an outcome of rational wealth-maximising behavior by slave-owners. The declining height of the free population was a result of reduced food intake in response to socio-economic processes associated with the onset of modern economic growth. These included an increase in the inequality of income distribution, urbanization and a rise in the relative price of food. However, these factors affected the slave economy less, or not at all (Komlos and Coclanis, 1997). The decision about how well to feed slaves depended primarily on the productivity of which would decline if nutritional standards were lowered. Slave prices reflect the capitalised value of the net returns to slaves, and the fact that during the antebellum decades slave prices increased by some 64 per cent relative to food prices lends support to the notion that increasing slave heights reflect higher nutritional standards, which, in turn, were a response to the expected value of higher slave productivity (Ransom and Sutch, 1988).

To make this intuition precise, we set out a theoretical model which analyses the time path of food allotments to a slave over his lifetime as the path that maximises the wealth of the slave-owner. We then examine the extent to which the empirical evidence is consistent with the implications of this model.


  • The Model
  • We begin with an intuitive description of the model and its main results. The slave's life can be viewed as falling into four stages:

    1. From birth until the point in time at which work starts, denoted by t1. This date is endogenous, since it depends on the slave's reaching a particular degree of physical strength and maturity, and this will depend on the time path of food allotment over this period.
    2. From t1 until the time he stops growing and reaches full physical maturity at date t2. Over this period he is both working and growing. We take this date as given exogenously, but the slave's physical state at this date will again be determined by the time path of food allotment.
    3. From t2 until he stops working at T. For sake of simplicity we assume his physical capacity remains constant over this period. The current food allotment during this period determines the slaves current productivity in line with the basic idea underlying "efficiency wage theory".
    4. From T until death. Since this phase of a slave's live represents a fixed cost to the slave-owner, we shall ignore it in the formal modelling.

    The slave-owner chooses optimal time paths of food allotments over each of the first three of these time periods, in the light of the contribution food makes to the level and growth of physical capacity of the slave, the slave's productivity as a function of his physical capacity, and the relative prices of food and the slave's output. If we regard height as an indicator of physical capacity, the solution to this problem should allow resolution of the puzzle with which we began this paper. We solve the problem formally for each of the three relevant phases of the slave's life, working backward from the last.


    1. Calibration of the Model and Numerical Results
    2. The optimal time paths of food allotment for the three phases should have an upward trend to explain the increase in slave heights in the antebellum period. In order to calibrate the model, we need price series for cotton, for food, and slave prices. The slave prices are hedonic price indices; we standardize for age, gender, known defects, reported skills, and geographical origin. Phyiscal capacity is measured by height, based on the data in Steckel (1995b); The observation period is 1800-1860. We start with Phase 3 by setting t2=18 and T=50 and find an obvious upward trend in food allotment. In Phase 2 we assume that the slave starts working at the age t1=8. Again, the resulting trend in food allotment for all age groups has a positive slope, and the same is true for Phase 1.


    3. Conclusions

    The puzzle concerning the increasing heights of slaves relative to the free population in the antebellum US can be explained by recognising the decision on food allocation to slaves as motivated by wealth maximization of slave-owners. The theoretical model makes precises the relationships among slave physical capacity, food allocation, output (cotton) and input (food) prices, exogenous factor productivity and slave prices. The evidence on slave prices and the time paths of food allotment is consistent with what we would predict.


    1The pattern is not perfectly uniform insofar as the heights of black soldiers in the Union Army did decline, but this could have been due to the fact that soldiers were drawn from both slave and free black populations. The share of each group in the sample is not known (Margo and Steckel, 1992).

    2 U.S. Department of Commerce, Bureau of the Census: Historical Statistics of the United States, Bicentennial Edition (1975), Part I, Series E 126.

    3 Wholesale price index (food), U.S. Department of Commerce, Bureau of the Census: Historical Statistics of the United States, Bicentennial Edition (1975), Part I, Series E 54.

    4 Data Source: ICPSR 7423: The New Orleans Slave Sample, 1804-1862; ICPSR 7421: Slave Sales and Appraisals, 1775-1865. The hedonic index is estimated based on a simple dummy model, where the dummies capture the different characteristics of the slaves. The age groups are 0-10, 11-15, 16-20, 21-30, and > 30 years. Following the codes in the New Orleans sample, the geographical origin is catured by four groups: slave exporting states, slave importing states, mxed states (North and South). Since the model does not distinguish between male and female slaves, we focus on the male slaves.



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